New York AGRICULTURAL EXPERIMENT STATION. 125 
WHAT SOAPS IN GENERAL ARE. 
Before presenting the results of analysis, we will consider 
briefly the chemistry of soaps. Soaps are made by treating 
fats or oils with a caustic alkali, caustic soda being used in mak- 
ing hard soap and caustic potash in making soft soap. A real 
chemical combination occurs between the alkali and the fat or 
oil. Thus a fat or oil is generally a mixture of several com- 
pounds, each of which contains glycerine in chemical combina- 
tion with certain acids, most commonly what are known as 
“fatty” acids. When a fat or oil is treated with caustic soda, 
the sodium takes the place of the glycerine and unites with the 
fatty acids, forming a sodium compound of each of the fatty 
acids, and the glycerine that was in combination is set free as 
glycerine. In some cases, boiling is necessary to cause the 
alkali and fatty acid to combine; in other cases, the action takes 
place at ordinary temperatures. A soap is, therefore, a chemical 
compound formed by the union of an alkali with the fatty acid 
or acids of a fat or oil. Other substances are frequently added 
to soaps for various purposes, such as resin, water, coloring 
matter, perfume, etc. 
EXPLANATION OF TERMS USED IN ANALYSIS OF SOAPS. 
The terms commonly used in expressing the results of analy- 
sis of a soap, when it is desired to determine its fitness for spray- 
ing purposes are the following. (1) Water, (2) fatty acids 
expressed as anhydrides, (3) sodium oxide combined as soap, (4) 
potassium oxide combined as soap, (5) resin, (6) free acid esti- 
mated as oleic acid, (7) free alkali. 
(1) Water in soap.—lIt is desirable to know the amount of 
moisture in soap in order to know its value for spraying pur- 
poses, since the greater the amount of water in the soap, the 
more soap will be needed to make a soap solution of a certain 
strength. 
(2) Fatty acids expressed as anhydrides.—Unéer this heating, 
we indicate simply the proportion of fatty acids present in the 
soap. : 
(3) Sodium oxide combined as soap.—In order to know the 
kind and amount of alkali present in a soap, it is necessary to 
